The invention relates to a welding method in which a body substantially open at opposite ends is formed from a flat metal sheet and welded along its edges. For example, roller seam welding involves forming the body with overlapping edges and feeding the region of overlap to welding rollers. The invention further relates to apparatus for carrying out the method.
It is known to form hollow cylindrical bodies from flat metal sheets, e.g. can bodies or ventilation pipes, the edges being butted against one another or an overlapping region of sheet metal being formed which is then joined by seam welding. As is known, seam welding involves the bodies to be welded being fed, preceding the welding zone, through a large number of rollers adapted to match the cross-section of the body being welded, with these rollers forming a passage which surrounds the body, or a guiding tool (so-called diabolo rolls according to Swiss Patent CH-A-671904). These roller guide tools maintain the shape of the body and press its longitudinal edges into a Z-shaped rail which takes care of the butt-jointed positioning or overlapping of the longitudinal edges which is required for welding. Seam welding then takes place by advancing the metal sheet through the guiding tools with the welding rollers operating on the overlap, and normally involves the use of wire electrodes.
In the case of metal sheets that incorporate reliefs or recesses, or that are composed of different thicknesses of material or else have been cut out in such a way that the end surface of the rounded body is not at right-angles to the longitudinal axis, or direction of the weld seam, these conventional roller guiding tools have been known to cause problems since there is no guarantee that the workpiece will be correctly guided and centred. Therefore to date such welds have not been produced using the conventional welding machines.
It is therefore an object of this invention to devise a method of welding bodies, more particularly sheet metal casings, by which it is possible to weld a body formed from a sheet metal blank of any desired shape and even metal sheet incorporating recesses or differences in material thickness or hardness.